In color diffusion transfer photographic elements, a method of effectively obtaining image densities is one of the very important technical factors in the field of color diffusion transfer photographic materials, for the purpose of, for example, (a) obtaining sharp images, (b) obtaining images in a moment as far as is possible by reducing the thickness of the photosensitive material as far as is possible, (c) improving sharpness byreducing the thickness of the layer as far as is possible similarly to (b) to shorten the diffusion distance of (d) producing color diffusion transfer phosotraphic elements at a low price, etc.
There are two major systems in instant photography at present. One is a system where dye developers are used (for example, U.S. Pat. Nos. 3,649,265, 3,161,506, 3,173,786, 3,253,915, etc.) and the other is a system which uses dye-releasing redox compounds (for example, U.S. Pat. No. 4,110,113).
These two different types of systems are essentially different in the manner of forming images and in the compositions of the photographic elements and developers used; as a consequence, the problems encountered and the consideration involved with these two different types of systems are quite different.
Dye developers which contain in the same molecule both the chromophoric system of a dye and a photographic silver halide developing moiety function both as a silver halide developing agent and as a dye in photographic diffusion transfer systems.
Dye developers are characterized by the art as being relatively non-diffusible in colloid layers such as hydrophilic organic colloids used in photographic emulsions at a neutral pH. However, they become diffusible in photographic elements in the presence of alkaline processing solutions. Thus, when an alkaline processing solution is applied to an exposed photographic element of the dye developer type, silver halide in exposed regions is developed and contiguous dye developers are immobilized, whereafter dye developers from unexposed (and undeveloped) areas of the photographic element diffuse and transfer to a receiving layer to yield a positive dye developer image. Such effects are described in U.S. Pat. No. 3,253,915.
In distinction to a dye developer base system as above explained, in a system where dye releasing redox compounds are used, the dye releasing redox compounds are mobilized, i.e., when a diffusion transfer photographic unit containing a dye releasing redox compound is imagewise exposed and developed in the presence of photosensitive silver halide emulsion, the dye releasing redox compound is oxidized in proportion to the amount of developed silver halide, the oxidized dye releasing redox compound is decomposed into a dye moiety and a non-diffusible moiety by an alkaline processing solution, and the dye moiety is mobilized and transferred to a receiving layer to yield a transfer dye image.
As a specific example, a cyan dye developer which theoretically develops only red-sensitive silver halide emulsion will also develop blue-sensitive or green-sensitive silver halide emulsion if development due to yellow and magneta dye developers, respectively, has not been completed by the time the cyan dye developer reaches these emulsions. Such development is obviously highly undesirable as such results in inter-image effects and it is highly desirable to provide a transfer system in which the dye is not attached to a "reactive" moiety as in a dye developer system so that the dye can diffuse throughout the system without becoming immobilized in the undesired or wrong emulsion layer.
To eliminate such undesirable inter-image effects, non-diffusible couplers which release a dye, i.e., dye releasing redox compounds, are used.
Reflecting the substntial difference in approach to forming images between the two systems, various problems which have been overcome in the dye developer system have also arisen in the dye releasing redox compound system, though due to different reasons.
For example, dye developers provide best photographic effects when used in combination with a hydroquinone type developing agent as taught in U.S. Pat. No. 3,253,915.
However, if hydroquinone developing agents are used together with dye releasing redox compounds, photographic properties are substantially harmed.
Further, it has been mentioned that onium compounds as disclosed in U.S. Pat. No. 3,161,506 are preferably used in formation of dye developer images. According to the disclosure of U.S. Pat. No. 3,161,506, the onium compounds interact with the dye developers to form salts thereof and the improvements in reduced color contamination, color drop off and minimum density obtained by their use are are at least due in part to the effect of such salt formation on the solubility and diffusibility of the dye developers. The onium compounds temporarily delay the migration of the dye developers so that the initial diffusion rates of the dye developers are reduced, yet more of the dye developers transfers from less exposed areas to increase the density. In this case, the onium compounds are employed in a large amount sufficient to form salts of the onium compounds, i.e., 0.2 to 15%, in an alkaline processing solution.
For color diffusion transfer photographic elements using a silver halide developing agent capable of causing cross-oxidation of a dye releasing redox compound, a method of increasing the activity of the silver halide developing agent capable of causing cross-oxidation of the above-described dye releasing redox compound, namely a method using the above-described silver halide developing agent having a low oxidation-reduction potential, is known as a method of obtaining images at a moment as far as is possible. However, since the silver halide developing agent is used in this case, cross-oxidation of the dye releasing redox compound with a non-electron oxidation product of the silver halide developing agent is difficult to carry out and, consequently, sufficient image densities are difficult to obtain.
Namely, when a silver halide developing agent having a low oxidation-reduction potential is used, the development rate of the coated silver halide becomes high, but cross-oxidation of the oxidation product of the silver halide developing agent with the dye releasing redox compound does not sufficiently advance and, consequently, images having a sufficient density cannot be obtained.
The present invention is, in essence, based on the discovery that when dye releasing redox compounds are used in combination with 1-phenyl-3-pyrazolidones or aminophenols and ammonium compounds in such an amount less than that as used in U.S. Pat. No. 3,161,506 that would not interact with dye releasing redox compounds and could thus not form salts of the ammonium compounds, excellent photographic properties are obtained.